Not everyone has the freedom to quit their job, small towns, limited skill sets, transportation issues, family issues, etc. etc. etc, otherwise the number would probably be at 75%.
But what if all employees are humans. And like humans, they are irrational in their criteria of what makes a boss "good". For example, they want bosses that never demand work from them and let them go home early every day. Even if they get this, their standards will adjust and they will take the same level of issue with smaller things. Being a boss and attempting to be liked by your employees is a lost cause and foolish endeavor.
But this is not true. If this is true no reputable company would have employees staying >3 years. If you're hired at a reputable company >1 year, chances are you do get offers or you have a greater chance to get it. Good bosses are rare, but they do exist.
My 3/4 bosses as intern were great. One guy was really incompetent, but he got me when the manager, who hired me, quit. So it’s almost ok.
After graduation the quality of managers varied greatly. There was a guy with 20 yeas experience, who took my mentoring very seriously. He fired me when I started my own company. Good decision actually! A boss before him was a great narcissist, if I were smarter, I would be able to play him and got higher. Not really the one to run from. Then there was a bunch of old dudes (totally incompetent) building big corp’s first electronics. They had no experience in the field and were really annoying. I quit. There was small company later with whole family in management: 2 sons, dad and mom. And a 2nd engineer. It was a part time position, so I was able to stay and suffer. No chance to stay with them for a 5 day workweek. My current manager is very restrictive. I can do things only old good way, all cost saving efforts and innovations are not needed. Heck, I could save company my early salary dozen times, but all the ideas were rejected.